Field
This invention relates generally to a scanning array antenna and, more particularly, to a hybrid scanning array antenna that electrically scans in elevation and mechanically scans in azimuth, where the antenna is compact to be suitable for airborne platform applications.
Discussion
There is a constellation of stationary geosynchronous communications satellites in orbit around the earth that are used for both commercial and military purposes. Adjacent satellites in the constellation are required to be some minimal distance or number of degrees apart so that uplink signals transmitted to a particular satellite in the constellation from ground stations or airborne platforms are not received and do not interfere with the adjacent satellites. In order to accomplish this, the transmission antennas that transmit the uplink signals need to have a beam width on the order of a few degrees and have high gain.
Active phased array narrow beam width antennas that are able to electronically scan in both the azimuth and elevation directions are available in the art for this purpose. Active phased array antennas have good antenna and radar cross-section (RCS) performance, but they are expensive. Further, the cost of active phased array antennas increases proportionally with the aperture size of the antenna. Generally, BLOS or SATCOM antennas require large aperture areas, which result in array antennas with thousands of individually phased-weighted and amplified antenna elements, which significantly increases the cost of the antenna.
For airborne platform satellite communications applications, it is known in the art to provide an antenna dish that is mechanically scanned in both the azimuth and elevation directions using a two-dimensional gimbal. Such dish antennas are typically large in size and are mounted under a radome extending from the aircraft skin. Because the radome extends from the aircraft it creates drag, which reduces fuel efficiency and reduces mission time on station. Additionally, the radome increases the aircraft's RCS, which causes the aircraft to become more visible on radar. Further, dish antennas often have poor aperture efficiency and high side-lobe levels for antennas designed to operate over wide instantaneous bandwidths. Transmit versions of dish antennas often require a high power traveling wave tube amplifier (TWTA) to amplify the transmit signal.